Method of explosively expanding sleeves in eroded tubes

ABSTRACT

The method comprises explosively expanding a first metallic sleeve into engagement with a severely eroded section of a tube and thereafter explosively expanding a second metallic sleeve of approximately the same diameter as the first sleeve into engagement with the first sleeve to cover cracks formed in the first sleeve due to excessive expansion of portions of the first sleeve resulting from the erosion-produced, tapering of the inner wall of the tube.

United States Patent Lieberman [45] Jan, 1, 1974 [54] METHOD OFEXPLOSIVELY EXPANDING 2,716,428 8/1955 Pennella 138/97 S V S [N ERODEDTUBES 2,966,373 12/1960 Yount 138/97 X 3,317,222 5/1967 [75] Inventor:Irving Lieberman, Covma, Calif. 3503,] 10 3/1970 Assignee: WhittakerCorporation LOS 3,562,887 2/1971 Schroeder et a1 29/421 X A l s, C 11.

nge e a 1 Primary ExaminerCharles W. Lanham Filedi 1972 AssistantExaminerV. A. DiPalma [2]] AppL NO: 311 492 Att0rneyDona1d E. Nist eta1.

57 ABSTRACT [52] U.S. C1. 29/401, 29/421, 137/15, 1

138/98 138/DIG 6 138/97 The method comprises explosively expanding afirst [511 lm. Cl B2'2d 19/10 B23p 7/00 metallic Sleeve engagement witha severely [58] Field of Search 29/401 R 1574 eroded section ofa tubeand thereafter explosively ex- 29/421 E 421 137/15. 138/97 98 D[G'panding a second metallic sleeve of approximately the same diameter asthe first sleeve into engagement with [56] References Cited the firstsleeve to cover cracks formed in the first sleeve due to excessiveexpansion of portions of the 2 1 m 927 :TATES PATENTS first sleeveresulting from the erosion-produced, taperay 285 54 2,445,273 7/1948Kennedym. 138/97 mg of the Inner wan of the tube 2,620,830 12/1952Schultz 138/97 10 Claims, 6 Drawing Figures T AQ Z Z 1 1 1 I I H 7METHOD OF EXPLOSIVELY EXPANDING SLEEVES I'N ERODED TUBES BACKGROUND OFTHE INVENTION tubes.

Tubes such as those employed in heat exhangers and the like are subjectto severe erosion from the fluids flowing therethrough. Such erosion isparticularly severe at and adjacent to the ends of such tubes with theerosion generally diminishing with distance into the tubes. Usually, theerosion extends about 4 inches into the tube. Because of the change inthe severity of the erosion with distance into the tube, the innersurface of the tube is given a conical or trumpet shape with theinternal diameter of the tube increasing as the end of the tube isapproached.

In the case of tubes which are not severely eroded, steel (or othermetal) sleeves can be expanded into the ends of the tubes by rolling orexposive means. However, when this is attempted on severely erodedtubes, the sleeves crack because the ends of the sleeves adjacent to theends of the tubes are expanded beyond their yield points. As a result,badly eroded tubes have had to be completely replaced. This, of course,is very expensive because of increased labor and material costs, andunit down time.

An alternative to replacement is to expand sleeves having an outer taperwhich approximates the taper of the eroded section of the tube. However,this method is very expensive because of the high cost of formingtapered tubing, particularly when that tubing has to be tailored to eachapplication.

SUMMARY OF THE INVENTION This invention is a method for expandingerosion resistant metal sleeves into severely-eroded tubes. This isaccomplished by inserting a first metallic sleeve into a tube within theeroded section of the tube and explosively expanding this sleeve intoengagement with the tube. Although the sleeve will fracturein the regionwhere it has to expand the most, this is overcome by inserting a secondmetallic sleeve into the first, expanded sleeve and explosivelyexpanding the second sleeve into engagement with that region of thefirst sleeve that fractured. The second sleeve has substantially thesame thickness and outside diameter as the first sleeve, but is ofshorter length since it can only be inserted part way into the firstsleeve which, when expanded into the tube, has a trumpet shape openingtoward that end of the tube into which the sleeves are inserted.

A principal advantage of this invention is that even heavily erodedtubes can be re-used for many years, instead of being replaced, so thata substantial cost saving is realized. Furthermore, this method isrelatively inexpensive since it employs standard tubing for the sleeves.I

DESCRIPTION OF THE DRAWING FIG. 1 is a sectioned view taken along aportion of the length ofa tube illustrating the inner wall produced byerosion.

FIG. 2 is a full end view of the tube of FIG. 1 taken in the direction22 of FIG. 1.

FIG. 3 is the same view as FIG. 1 but further illustrates thepositioning of a first sleeve and explosivecontaining insert within thetube.

FIG. 4 is the same view as FIG. 1 and it shows the first sleeve expandedagainst the tube.

FIG. 5 is the same view as FIG. 4 and further shows the positioning of asecond sleeve within the tube.

FIG. 6 is the same view as FIG. 4 and further shows the second sleeveexpanded into engagement with the first sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, the numeral 10designates a highly eroded tube, e.g., a carbon steel tube, which has anominal or non-eroded thickness A which is usually on the order of 0.040in. to 0.150 in. for heat exchanger tubes. However, due to erosion, thethickness of the tube 10 can decrease by about 0.045 in. at the end 12of the tube 10. This decrease in thickness generally occurs along alength of about 4 in. for heat exchanger tubes so that the inner surface14 of the tube 10 becomes highly tapered as shown by FIG. 1 and FIG. 2.As used herein, the term highly eroded tube means a tube in whicherosion has produced an internallytapered surface which defines a boresection which is too large to permit explosive expansion of acylindrical sleeve which is receivable by the non-eroded portion of thetube, without fracturing.

To provide the tube 10 with a new inner surface or liner, a sleeve orferrule 16 is formed from, preferably, an erosion-resistant metal suchas stainless steel. The sleeve 16 has the same cross-sectional shape asthe tube 10. In general, the OD. and thickness of the sleeve 16 areselected so that the sleeve will expand beyond its plastic limit, butwill not expand beyond its yield strength limit in that part of the tube10 having an original ID. of B. This is well-known in the art and doesnot constitute a part of this invention. Hereinafter, the termexplosively expandable sleeve will be used to designate a sleeve havinga diameter and thickness such that the sleeve can be explosivelyexpanded against a parallel surface, such as that section of the innertube wall having a nominal diameter, without fracturing. Preferably, thesleeve 16 has an OD. which is less than, but substantially equal to thenominal ID. of the tube 10 so that the sleeve 16 is slidably received bythe tube 10 along its non-eroded length.

The length of the sleeve 16 is selected so that it will extend inwardlyfrom the end 12 of the tube 10 to a point beyond the end of the taperedsection of the tube wall 14 as shown in FIG. 2. That is, the sleeve 16extends from the tube end 12 into the portion of the tube having anominal ID. of B. This, inter alia, ensures that the eroded section willbe completely covered by the sleeve 16.

The outer surface of the sleeve 16 is preferably provided with anannular taper 17 extending from the inner end of the sleeve for adistance of about 0.5 in.-l in. This taper 17 is reversed by theexplosive expansion of the sleeve 16 and appears on the interior surfaceof the sleeve 16. This serves to fair the sleeve wall into the tube wallto improve fluid flow past the tube/sleeve innermost juncture.Additionally, the outermost end of the sleeve 16 may be flaired toensure that the eroded area adjacent to the end 12 of the tube 10 iscovered when the sleeve 16 is expanded.

After the sleeve 16 is positioned within the tube 10. aforce-transmitting insert 18 such as is described in us. Pat. No. 3,411,198, issued Nov. 19,1968 and US. Pat. No. 3,503,l 10, issued Mar. 3 ll970, and containing an explosive 20 positioned within the sleeve 16 asshown in FIG. 3. A detonator 22 is placed in direct contact with theexplosive 20 as shown in FIG. 3, to initiate detonation of theexplosive. When the latter occurs, the sleeve 16 is expanded intoengagement with the inner wall 14 of the tube 10 as shown in FIG. 4.

The sleeve 16 expands against that portion of the inner wall 14 having anominal diameter B and for some distance along the inner wall 14 towardsthe tube end 12 without fracturing. However, in the region adjacent tothe tube end 12, the sleeve 16 is caused to expand beyond its yieldstrength limit due to the tapering of the inner wall 14. This expansionproduces fracturing or cracks 26 (FIG. 4) in the sleeve 16.

To cover the cracks 26 and to provide a relatively continuous innerliner surface, a second sleeve 28 is inserted within the expanded sleeve16. The inner sleeve 28 has an OD. and thickness which are substantiallyequal to those of the expanded sleeve 16. The length of the inner sleeve28 is made to aproximate the distance from the tube end 12 to the innerend of the eroded section of the inner wall 14. This usually means thatsome force is required to force substantially the total length of thesleeve 28 into the tube 10. In some cases, the sleeve 28 may have to beshortened slightly. The resulting forcefit ensures concentric alignmentof the sleeve 28 with the longitudinal axis of the tube 10. Preferably,the inner end 30 of the sleeve initially is externally tapered tointernally taper it by expansion as described with reference to theouter sleeve 16.

The inner sleeve 28 is exposively expanded into engagement with theexpanded sleeve 16 using an insert as described herein with reference toFIG. 3. The result of this second expansion is shown in FlG. 6. That is,the tube 10 is provided with a liner having a double thickness extendinginwardly from the tube end 12 to substantially the location along thetube length where the tube thickness is substantially that of thenon-eroded tube. From that location inward to the inner end of the outersleeve 16, the liner has a single thickness.

If the erosion is so severe that the inner sleeve 28 also cracks, athird sleeve (not shown) may be employed as described in connection withthe inner sleeve 28.

This invention will be further described by the following Example.

EXAMPLE A number of stainless steel sleeves were explosively expandedinto highly eroded carbon steel tubes using the method described herein.

The tubes had a nominal ID. of 0.435 in. which increased over a distanceof about 4 in. to an ID. at the end of the tubes of about 0.530 in. Thenominal CD. of the tubes was about 0.550 in.

The first sleeve was 6 in. long and the second sleeve was 4 in. long.Both sleeves were 0.016 in. thick and had an CD. of 0.430 in.Additionally, both sleeves were provided with an external taper at theirinnermost ends of about 0.5 in. in length.

The tubes have been used in a heat exchanger for several months withexcellent results.

I claim:

1. A method of providing a tube with a liner wherein said tube has ahighly eroded, internally-tapered section, said method comprising thesteps of:

inserting a first metal sleeve into said tube so that said first sleeveis substantially coextensive with both said eroded section and anadjacent section of said tube having a nominal internal diameter, saidfirst sleeve being explosively expandable against said adjacent sectionof said tube;

explosively expanding said first sleeve into engagement with said tube;

inserting a second metal sleeve within said first sleeve, said secondsleeve characterized by being explosively expandable into engagementwith said section of said tube having said nominal diameter and having alength substantially as long as is permitted by the bore defined by saidexpanded first sleeve; and

explosively expanding said second sleeve into engagement with said firstsleeve.

2. The method of claim 1 wherein said second sleeve has an outerdiameter substantially equal to that of said first sleeve.

3. The method of claim 1 wherein the outer diameter of said first sleeveis substantially equal to but less than said nominal internal diameterof said tube.

4. The method of claim 1 wherein the innermost ends of said first andsecond sleeves are provided with an external taper which reverses uponexpansion of said inserts to provide a more continuous surfacetransition from said expanded second sleeve to said expanded firstsleeve to said tube.

5. The method of claim 1 wherein said second sleeve is expanded beyondits yield point and wherein a third sleeve is explosively expanded intoengagement with said second sleeve, said third sleeve having an outerdiamter substantially equal to that of said first and second sleeves andhaving a length as long as that which is receivable by said expandedsecond sleeve.

6. The method of claim 1 wherein said sleeves comprise anerosion-resistant metal.

7. The method of claim 1 wherein said second sleeve is force-fitted intosaid expanded first sleeve prior to expanding said second sleeve.

8. A method of providing a tube with a liner wherein said tube has ahighly-eroded, internally-tapered section, said method comprising:

inserting a first erosion-resistant metal sleeve into said tube, saidsleeve being coextensive with said eroded section and with an adjacentsection having a nominal diameter and having an outer diametersubstantially equal to but less than said nominal diameter of said tube;

explosively expanding said sleeve into engagement with said tube tofracture said first sleeve adjacent to its end of greatest expansion;

force-fitting an end of a second erosion-resistant,

metal sleeve into said expanded first sleeve, said second sleeve havinga diameter and thickness substantially equal to those of said firstsleeve and having a length extending from the region of said force fitsubstantially to said end of geatest expansion of said first sleeve; and

explosively expanding said second sleeve into engagement with said firstsleeve.

9. The method of claim 8 wherein said force-fitted end of said secondsleeve is externally tapered.

10. The method of claim 8 wherein the innermost end of said first sleeveand said force-fitted end of said second sleeve are externally tapered.

1. A method of providing a tube with a liner wherein said tube has ahighly eroded, internally-tapered section, said method comprising thesteps of: inserting a first metal sleeve into said tube so that saidfirst sleeve is substantially co-extensive with both said eroded sectionand an adjacent section of said tube having a nominal internal diameter,said first sleeve being explosively expandable against said adjacentsection of said tube; explosively expanding said first sleeve intoengagement with said tube; inserting a second metal sleeve within saidfirst sleeve, said second sleeve characterized by being explosivelyexpandable into engagement with said section of said tube having saidnominal diameter and having a length substantially as long as ispermitted by the bore defined by said expanded first sleeve; aNdexplosively expanding said second sleeve into engagement with said firstsleeve.
 2. The method of claim 1 wherein said second sleeve has an outerdiameter substantially equal to that of said first sleeve.
 3. The methodof claim 1 wherein the outer diameter of said first sleeve issubstantially equal to but less than said nominal internal diameter ofsaid tube.
 4. The method of claim 1 wherein the innermost ends of saidfirst and second sleeves are provided with an external taper whichreverses upon expansion of said inserts to provide a more continuoussurface transition from said expanded second sleeve to said expandedfirst sleeve to said tube.
 5. The method of claim 1 wherein said secondsleeve is expanded beyond its yield point and wherein a third sleeve isexplosively expanded into engagement with said second sleeve, said thirdsleeve having an outer diameter substantially equal to that of saidfirst and second sleeves and having a length as long as that which isreceivable by said expanded second sleeve.
 6. The method of claim 1wherein said sleeves comprise an erosion-resistant metal.
 7. The methodof claim 1 wherein said second sleeve is force-fitted into said expandedfirst sleeve prior to expanding said second sleeve.
 8. A method ofproviding a tube with a liner wherein said tube has a highly-eroded,internally-tapered section, said method comprising: inserting a firsterosion-resistant metal sleeve into said tube, said sleeve beingcoextensive with said eroded section and with an adjacent section havinga nominal diameter and having an outer diameter substantially equal tobut less than said nominal diameter of said tube; explosively expandingsaid sleeve into engagement with said tube to fracture said first sleeveadjacent to its end of greatest expansion; force-fitting an end of asecond erosion-resistant, metal sleeve into said expanded first sleeve,said second sleeve having a diameter and thickness substantially equalto those of said first sleeve and having a length extending from theregion of said force fit substantially to said end of greatest expansionof said first sleeve; and explosively expanding said second sleeve intoengagement with said first sleeve.
 9. The method of claim 8 wherein saidforce-fitted end of said second sleeve is externally tapered.
 10. Themethod of claim 8 wherein the innermost end of said first sleeve andsaid force-fitted end of said second sleeve are externally tapered.